Method and apparatus for determining the volume of a body cavity in real time

Abstract

A method and apparatus for determining the volume of a fluid-filled cavity in a patient's body in real time from an ultrasound image. An ultrasound display of the cavity and the surrounding tissue is obtained. The ultrasound display includes a sequence of ultrasound images. The user traces a fixed region of interest around the image of the cavity at the largest volume for which the volume determination is to be made. The region of interest is subdivided into a predetermined number of segments. Each pixel of the ultrasound image, at least within the region of interest, is classified as a fluid pixel or a tissue pixel. The area of fluid pixels within each segment is determined. The volume of the cavity is calculated from the area of the fluid pixels within each segment of the region of interest using the method of disks. The volume is determined for each ultrasound image in the sequence of ultrasound images to provide the volume of the cavity in real time.

What is claimed is: 
     
       1. A method for determining the volume of a fluid-filled cavity in a patient's body in real time, comprising the steps of: a) obtaining a real time, two-dimensional ultrasound display of a fluid-filled cavity and the surrounding tissue, said ultrasound display comprising a sequence of ultrasound images on a display screen;   b) determining parameters of a fixed, user-defined region of interest surrounding the ultrasound display of the cavity at the largest volume for which said volume determination is to be made;   c) subdividing said region of interest into a predetermined number of segments which entirely fill said region of interest, each of said segments having a height;   d) classifying each pixel, at least within said region of interest, of an ultrasound image in said sequence of ultrasound images as a fluid pixel which represents fluid or a tissue pixel which represents tissue;   e) determining an area of fluid pixels within each segment of said region of interest;   f) calculating the volume of said cavity from the area of fluid pixels within each segment of said region of interest; and   g) repeating steps d) through f) for each ultrasound image of said sequence of ultrasound images to provide the volume of said cavity at each of the times when said ultrasound images were obtained.   
     
     
       2. A method as defined in claim 1 wherein said cavity comprises a ventricle of the human heart and said fluid comprises blood. 
     
     
       3. A method as defined in claim 1 wherein the step of calculating the volume of said cavity comprises the steps of approximating a volume of said cavity within each segment by a disk having a height equal to the height of said segment and a diameter equal to the total area of said fluid pixels dividing by the height, calculating the volume of the disk in each segment of said region of interest, and summing the volumes of the disks in the segments of said region of interest to provide the volume of said cavity. 
     
     
       4. A method as defined in claim 1 wherein the step of determining parameters of said fixed region of interest includes defining a long axis of said region of interest and wherein the height of each segment of said region of interest is defined along said along axis. 
     
     
       5. A method as defined in claim 1 wherein the step of determining parameters of said region of interest includes determining the coordinates of a boundary of said region of interest, determining a long axis of said region of interest and determining an angle between a normal to said long axis and a horizontal axis of said display screen, and wherein the step of subdividing said region of interest includes subdividing said region of interest by spaced lines normal to the long axis. 
     
     
       6. A method as defined in claim 5 wherein the step of subdividing said region of interest includes subdividing said region of interest into 20 segments having parallel boundaries normal to said long axis. 
     
     
       7. A method as defined in claim 6 wherein said segments have equal heights along said long axis. 
     
     
       8. A method as defined in claim 1 wherein the step of obtaining an ultrasound display includes transmitting and receiving ultrasound energy along a plurality of scan lines and wherein the step of determining the total area of fluid pixels includes accumulating areas of fluid pixels within each segment along each scan line to provide the total area of fluid pixels within each segment. 
     
     
       9. A method as defined in claim 8 wherein the step of determining the area of fluid pixels with each segment of said region of interest further includes the steps of storing a start depth, a stop depth and a segment number for each segment along each scan line, and storing the area of fluid pixels within each segment in an accumulator corresponding to said segment number when a depth along each scan line between said start depth and said stop depth is being scanned. 
     
     
       10. Apparatus for determining the volume of a fluid-filled cavity in a patient's body in real time comprising: means for obtaining a real time, two-dimensional ultrasound display of a fluid-filled cavity and the surrounding tissue, said ultrasound display comprising a sequence of ultrasound images on a display screen;   means for determining parameters of a fixed, user-defined region of interest surrounding the ultrasound display of the cavity at the largest volume for which said volume determination is to be made;   means for subdividing said region of interest into a predetermined number of segments which entirely fill said region of interest, each of said segments having a height; and   means for processing each ultrasound image of said sequence of said ultrasound images to provide the volume of said cavity at each of the times when said ultrasound images were obtained, said means for processing comprising: means for classifying each pixel, at least within said region of interest, of an ultrasound image in said sequence of ultrasound images as a fluid pixel which represents fluid or a tissue pixel which represents tissue;   means for determining an area of fluid pixels within each segment of said region of interest, and   means for calculating the volume of said cavity from the area of fluid pixels within each segment of said region of interest.     
     
     
       11. Apparatus as defined in claim 10 wherein said means for determining parameters of said fixed region of interest includes means for determining the coordinates of a boundary of said region of interest, means for determining a long axis of said region of interest and means for determining an angle between a normal to said long axis and a horizontal axis of said display screen and wherein said means for subdividing said region of interest includes means for subdividing said region of interest by spaced lines normal to the long axis. 
     
     
       12. Apparatus as defined in claim 10 wherein said means for obtaining an ultrasound display includes means for transmitting and receiving ultrasound energy along a plurality of scan lines and wherein said means for determining the area of fluid pixels includes means for accumulating areas of fluid pixels within each segment along each scan line to provide the area of fluid pixels within each segment. 
     
     
       13. Apparatus as defined in claim 12 wherein said means for determining the total area of said fluid pixels further includes means for storing a start depth, a stop depth and a segment number for each segment along each scan line and means for storing the area of fluid pixels within each segment in an accumulator corresponding to said segment number when a depth along each scan line between said start depth and said stop depth is being scanned. 
     
     
       14. Apparatus as defined in claim 10 wherein said means for calculating the volume of said cavity comprises: means for approximating the volume of said cavity within each segment of said region of interest by a disk having a height equal to the height of said segment and a diameter equal to the area of said fluid pixels within each segment divided by the height;   means for calculating the volume of the disk in each segment of said region of interest; and   means for summing the volumes of the disks in the segments of said region of interest to provide the volume of said cavity.